Closed Circuit Television (CCTV) Glossary

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AC
Alternating Current

ACCESS CONTROL SYSTEM
Electronic system used to allow, restrict and track
the movement of people through entry/exit points
in a site. This is achieved through the use of electronic
individual codes, keys or cards etc, to release
a locking mechanism.

ACTIVITY DETECTION
A feature built into some multiplexers, which is
used to detect movement within a camera's field
of view that is then used to improve camera recording
update rate.

AGC (AUTOMATIC GAIN CONTROL)
An electronic circuit that is used to boost the
video signal in a camera in low light conditions.
Use of this feature will usually give a "noisy"
or grainy picture. When comparing camera specifications
always use data with AGC off.

ALARM INTERFACE
A facility which allows the use of external alarm
equipment such as PIR's, magnetic contacts etc to
be connected to CCTV equipment so that when the
alarm is activated the CCTV equipment will automatically
carry out a pre programmed function such as switching
to record a given camera.

ALC (AUTOMATIC LIGHT CONTROL)
A feature of an Auto Iris lens used to adjust the
between peak and average voltage which will emphasise
detail in bright areas (peak), or shadows (average).

ALGORITHMS
Complex mathematical formulae or rules used to solve
complex problems in CCTV they are used to achieve
digital compression of a video picture.

ALIASING
Also known as Moiré patterning. This is an
effect that occurs when an analogue signal is sampled
digitally at a sampling frequency less than twice
the signal frequency. The effect can be minimised
by a technique known as optical low-pass filtering.

ANALOGUE SIGNAL
A signal in which the level is represented by a
directly proportional voltage. In video the cameras
scene is represented by varying the voltage in the
video signal where the voltage is directly proportional
to the light level.

ALKALINE BATTERY
DC power source with a longer life than a standard
battery. Cannot be recharged.

AMPLITUDE
Expression of the strength of a video signal at
a given point. Measured in Volts.

ANGLE OF VIEW
Represents the area of a scene (maximum horizontal
and vertical angle) that can be seen through a lens.
Measured in degrees.

APERTURE
The light gathering part of a lens. The size of
the aperture is controlled by the Iris. Aperture
size is expressed as an "f" number. The lower the
"f" number the greater the amount of light gathered
by the lens.

ASPECT RATIO
The ratio between the width and height of a video
picture. The standard Aspect Ratio for CCTV Monitors,
NTSC and PAL systems is 4:3.

ASPHERICAL LENS
A type of lens, which has a non-spherical shape.
It is harder and more expensive to manufacture,
but it offers certain advantages over a normal spherical
lens.

ATTENUATION
The decrease in magnitude of a signal, as it travels
through a medium. Used to describe signal loss in
a transmission system. Measured in decibels (dB).

AUDIBLE DETECTOR
A device used to detect sound. In CCTV system it
can be interfaced with a switcher to switch on a
nominated camera when the detector is activated.

AUTO BALANCE
System used in colour cameras to detect and automatically
correct errors in the amplitude of colour signals.

AUTO IRIS (AI)
An automatic method of varying the size of a lens
aperture to allow the correct amount of light to
fall on the imaging device. The lens Includes a
tiny motor and amplifier, which are used to maintain
a one-volt Peak to peak video signal.

AUTO PAN
A feature of a pan and tilt head or dome, which
allows the camera to pan continually between two
preset points.

AVERAGE VIDEO SIGNAL
Represents the average light level of a picture
and is used to open or the iris in an Auto Iris
lens.

BACK-FOCUS
A fine mechanical adjustment in a camera that is
used to adjust the imaging device relative to the
lens to ensure that it is at the exact focal point
for the lens fitted. This adjustment is especially
important when fitting a zoom lens.

BACKLASH
An effect noticed in Pan and Tilt units, whereby
the unit does not come to a smooth stop at the end
of the pan movement. This is usually caused by play
in the mechanical components of the unit or by attempting
to bring the unit to an instant stop.

BALANCED SIGNAL
This is a video signal that has been converted to
enable it to be transmitted along 'twisted pair'
cables. Usually used where the signal has to be
transmitted over long distances, which would produce
unacceptably high losses in Coaxial cable.

BANDWIDTH
The frequency range required to carry an electronic
signal without attenuation or loss.

BARREL DISTORTION
A distortion in a monitor due to non uniform scanning
which causes the image to appear to bulge outward
like a barrel.

CABLE COMPENSATED AMPLIFIER
High frequency signals are attenuated when transmitted
through cables. A Cable Compensated Amplifier boosts
the high frequency signals depending on the cable
distance. This ensures the minimum video loss.

CABLE CORE
The central part of the cable, which actually carries
the video, power and control signals. This can be
constructed as a single conductor, or from wire
strands.

CCIR
Commitee Consultatif International des Radiocommunique.
European standardisation body that has set the standards
for television signals in Europe. 625 lines, 25 frames per second.

CCTV
Closed Circuit Television. Television system intended
to be viewed by restricted personnel and with a
dedicated purpose. Pictures from a CCTV system are
not intended to be broadcast for general viewing.

CCVE
Closed Circuit Video Equipment. Alternative term
for CCTV.

CFA
Colour Filter Array. Optical pixel filters used
in single chip colour CCD cameras, to produce the
colour components of a video signal.

CHANNEL SEPARATION
The term for the separation of signals when multiplexed
at different frequencies for transmission down a
single cable.

CHROMATIC ABERRATION
Optical term, which refers to the distortion of
an image as a result of a scattered focal point
caused by a defect in a lens. A combination of lens
can be used to correct this effect.

CHROMINANCE SIGNAL
The part of the video signal that contains the colour
information. In composite video The chrominance
signal is multiplexed at a higher frequency than
the signal and transmitted down the same cable.
In S-VHS this signal is transmitted along a separate
cable.

CLADDING
The outer part of a fibre optics cable. The cladding
is less dense than the central core, and acts as
an optical barrier to prevent the transmitted signal
from leaking away from the core.

C-MOUNT
Standard lens mounting with a 17.526mm back flange
(distance between the lens mount and the focal point).
Normally used on 2/3" and 1" cameras and lenses.

COAXIAL CABLE
Term for cable in which two or more conductors share
the same axis. Normally consists of a single inner
core and an outer shield. This is the standard cable
used to carry video signals in CCTV installations,
because it does not produce and is not influenced
by external fields.

COLOUR STRIPE FILTER
A filter that is placed in front of a colour CCD
chip to break up the light into the basic colours
(Red, Green, and Blue) The individual colours are
then directed at different pixels on the chip.

COMMON SYNC
Device used to synchronise cameras by generating
a synchronising pulse that is sent to all cameras
connected to it.

COMPOSITE VIDEO
The complete video signal, comprising both the video
and sync information.

CONCAVE LENS
Type of lens in which the light rays passing through
it are made to diverge by the inward curve of the
glass surface.

CONDUIT
Plastic or metallic pipe, which is used to conceal
and protect cables and wiring.

CONTRAST
The difference in intensity between the darkest
and the brightest parts of an image.

CONTRAST CONTROL
The control on a monitor used to change the contrast
by varying the amplitude of the video signal.

CONVEX LENS
Type of lens in which the light rays passing through
it are made to converge by the outward curve of
the glass surface.

COVERT CAMERA
Type of CCTV camera, which is concealed to allow
video recordings to be made without the knowledge
of the subjects.

CPU
Central Processing Unit. The heart of a computer
or computer based device.

CRIMPING
Term used to describe the process of joining a cable
to a connector without screwing or soldering. Requires
a special crimping tool to ensure a proper connection.

CRO
Cathode Ray Oscilloscope (see Oscilloscope).

CROSSTALK
Noise generated by the interference between adjacent
video, audio or data signals in a multiplexed signal.

CS-MOUNT
Standard lens mounting with a 12.5mm back flange
(the distance between the lens mount and the focal
point) Normally used on modern ¼", 1/3",
and ½" cameras and lenses.

DARK CURRENT
Leakage signal from a CCD sensor in the absence
of incident light.

DARK NOISE
Noise caused by the random (quantum) nature of the
dark current.

DECIBEL (DB)
A logarithmic ratio between two electrical signals
or values. Usually refers to power, but can also
be used for voltage and current.

DC
Direct Current.

DE-MULTIPLEXING
The process of separating different video, audio,
or data signals, which were multiplexed at source.

DEPTH OF FIELD
The distance between the nearest and furthermost
object in a scene which appear in sharp focus. Depth
of field varies depending on the f-stop and focal
length of a lens. Depth of field increases when
the f-stop is greater, the focal length shorter
or the distance to the object is increased.

DIELECTRIC
An insulating (non-conductive) material. Found between
the inner core and outer shield of a co-axial cable.

DIGITAL SIGNAL
An electronic signal, which is represented by binary
numbers, and that, can be processed by a microprocessor,
or stored in an electronic memory.

DOME
Term used to describe a type of camera housing made
of smoked glass or plastic usually containing a
pan and tilt head and used for discreet surveillance.

DOS
Disk Operating System. A software package that makes
a computer work with its hardware devices such as
hard drive, floppy drive, screen, keyboard, etc.

DUPLEX
A system that is capable of handling two channels
of information simultaneously. In CCTV, duplex is
used to describe a multiplexer that can record in
multiplex mode whilst simultaneously displaying
multi-screen pictures.

DWELL TIME
When relating to video switchers this is the time
that a picture remains on a monitor before being
replaced by the next picture.

EAS
Electronic Article Surveillance. System used in
retail stores to prevent shoplifting by attaching
tags to the merchandise, which activate an alarm
when passed through detectors. These systems are
often interfaced with CCTV systems.

EBU
European Broadcasting Union.

EIA
Electronics Industry Association. American Association
that sets the standard for video broadcast in the
USA and Canada (525 lines, 30 frames per second).

ELECTRON BEAM
A concentrated flow of electrons in a nominated
direction.

FRAME
Basic unit of a motion picture, made up of 2 fields
or 625 lines (in a PAL system).

FRAME INTERLINE CHIP
A type of CCD imaging device, which is expensive
to manufacture and is currently used in broadcast
quality cameras. This type of chip overcomes many
of the shortcomings of the existing CCD chips used
in CCTV cameras.

FRAME STORE
An electronic device used to capture and digitally
store a video image. Can be a stand-alone unit or
incorporated in other equipment such as fast scan
transmitters or video motion transmitters.

FRAME SWITCHER
A basic form of multiplexer, which can be used to
record multiple cameras on a single VCR.

FRAME TRANSFER
A type of CCD Imaging device in which the pixels
have a dual role of sensing the light and transferring
the charge. This can result in picture smearing,
which is a major shortcoming of this device.

GALVANOMETER
In CCTV this term refers to a method of operating
an auto iris lens. The changing light level causes
a change in the current induced into a minute coil,
which in turn causes movement in the Iris diaphragm.

GAMMA CORRECTION
A method of correction used in cameras to balance
the brightness seen by a camera to that of the monitor.

GEN-LOCK (EXTERNAL SYNC)
A method of synchronising a number of cameras in
a system to ensure that they all produce fields
at the same time. This is used to prevent picture
"bounce" when switching between cameras and can
improve the overall quality and update time of recordings
when using switchers or multiplexers.

GROUND LOOP CURRENT
In CCTV this term refers to a current that is produced
in a cable as a result of a difference in earth
potential existing at each end of the cable. The
result of this is noise (interference) introduced
in the signal.

GROUND LOOP INSULATOR
A transformer with no direct connection between
the inputs and outputs, used to eliminate Ground
Loop Currents.

GUI
(Graphical User Interface). A term used to describe
the interface between a computer screen and the
user. Now used in CCTV Systems to describe features
such as touch screen control of systems and equipment.

HARDWIRED
Refers to a method of controlling CCTV equipment
by using multi-cored cable run between the controller
and device to be controlled. Only used where the
distance between controller and controlled device
is short.

HERTZ
The unit of measurement for frequency in a signal.
1 Hertz = 1 cycle per second.

HOMING SWITCHER
Term used to describe a sequential switcher with
only one output.

HORIZONTAL RESOLUTION
The number of vertical lines that can be resolved
in a picture.

HORIZONTAL SHIFT REGISTER
Part of the CCD image device to which the charge
from the pixels is transferred line by line. This
charge is then converted into an analogue video
signal.

ILLUMINANCE
The amount of light, which falls onto a given surface
area. Measured in lux.

IMAGING DEVICE
A vacuum tube or solid state device in which the
vacuum tube light sensitive face plate, or solid
state light sensitive array, provides an electronic
signal from which an image can be created.

IMAGE INTENSIFIER
A devise used to intensify light through the use
of light sensitive phosphor screens. Used to intensify
camera performance under low light conditions.

IMPEDANCE
The total opposition to current flow in an a.c.
electrical circuit. Measured in Ohms.

INDEX OF REFRACTION
The ratio between the angle of incidence to the
angle of refraction of light. Index varies depending
on the density of the medium. The denser the medium,
the higher the index.

INFRARED LIGHT
Light produced at the red end of the spectrum. Not
visible to the naked human eye.

INFRARED ILLUMINATOR
Light source, which emits light in the infrared
part of the spectrum. Used to illuminate scenes
to provide views at night from infra sensitive monochrome
cameras.

INFRARED TRANSMISSION
Method of transmitting signals using an infrared
beam. Allows CCTV signals to be transmitted where
cables cannot be run. Signals can be degraded over
long distances or in adverse weather conditions.

INTERFERENCE
Effect caused by the introduction of unwanted electrical
signals into an electrical circuit. In CCTV this
results in "noise" in the signal or picture, which
disrupts the picture.

INTERLACING
The process of combining odd and even fields to
form a frame.

INTERLINE TRANSFER
A type of CCD imaging device in which the charge
is processed according to the amount of light falling
on the sensors and then transferred immediately.
This is the most common form of imaging device used
in current CCTV systems.

IP RATING
Index of protection that refers to the level of
protection provided by equipment housings, against
the ingress of dust or moisture.

IRIS
The part of a lens that is used to control the amount
of light that passes through the lens and onto the
imaging device.

ISDN
(Integrated Services Digital Network). Telecommunications
network that is capable of transmitting digital
signals at speeds of up to 128kb/sec.

LAN
(Local Area Network). Means of connecting a number
of computers to enable communication between each
device connected to the network.

LASER
(Light Amplification by Stimulated Emission of Radiation).
In CCTV this source of exceptionally pure light
can be used to transmit signals along fibre optic
cables, providing very high quality signal and data
transmission.

LED
(Light Emitting Diode). A semiconductor that produces
light when stimulated by an electric current. In
CCTV these are used as the light source in some
fibre optic transmission systems, and as light the
light source for illuminating scenes for use with
Monochrome cameras.

LENS
An optical device for focusing light onto the imaging
device in a camera.

LENS CALCULATOR
A calculator used to calculate the most suitable
lens to provide an image of a given scene when used
with a specific camera.

LENS HUNTING
A problem encountered when an auto iris lens opens
and closes alternatively because it is unable to
find the correct level.

LENS MOUNT
See C-mount or CS-mount.

LENS WHEEL
See Lens calculator.

LIGHT SENSOR
A device that is activated when a preset amount
of light is present on the sensor. Used to switch
on/off infrared illuminators.

LINE
The basic unit of a frame or field containing the
charge, which is proportional to the light falling
at various points on the scanning line.

LINE-LOCKED
Refers to a method of synchronising cameras to a
common AC frequency.

LOOPING SWITCHER
Refers to a type of switcher where signals are looped
through the switcher without being affected by the
operation of the switcher itself.

MAGNIFICATION RATIO
The ratio between the focal length of a lens and
the focal length of a standard angle lens. Indicates
the magnification of the image when compared to
an image from a standard angle lens.

MANUAL IRIS
Type of lens that requires manual focusing.

MATRIX SWITCHER
Advanced type of switcher in which a signal from
any input can be switched to any number or combination
of outputs. Generally used in larger and more complex
systems the matrix will usually also incorporate
a range of additional advanced features.

MICROWAVE TRANSMISSION
A method of transmitting signals using a microwave
frequency link. Not affected by adverse weather
but requires direct line of site. A licence may
be required to operate a microwave frequency system.

MODEM
Derived from the term Modulate-Demodulate. A modem
is used to convert between analogue and digital
signal to then transmit and receive the signals
over the PSTN network.

MOIRÉ PATTERN
An unwanted effect that appears in the video picture
when a high frequency pattern is looked at with
a CCD camera that has a pixel pattern close (but
lower) to the object pattern.

MULTIPLEX VIDEO RECORDING
The condensed recording of more than one video signal
on a single videotape, or hard disk drive.

MULTIPLEX
The concept of transmitting several signals on a
single channel.

MULTIPLEXER
A device that combines a number of signals into
one. Often used in CCTV to describe a device that
is primarily used to multiplex several video signals
into one for the purposes of recording or microwave
transmission. It can also refer to a fibre optics
multiplexer which combines a number of video signals
into one in order to transmit all of them via a
single fibre cable.

N/C AND N/O ALARMS
Refers to Normally Closed and Normally Opened contacts.
It is usually used to describe alarms in CCTV.

NA
Numerical Aperture. A measure of the angular acceptance
of light incoming into a fibre optics cable, in
the form of a cone. It is expressed as the square
root of the difference of the squares of the indices
of the core and the cladding.

NBS
National Bureau of Standards (USA).

ND FILTERS
Neutral Density filters are optical filters that
attenuate the light a number of times. This attenuation
is equal for all the wavelengths therefore it does
not change the colour balance of an image, hence
the term neutral.

NIT
A photometric unit for measuring luminance. One
nit is equal to one candela per square metre of
a projected surface area.

NOISE
An unwanted signal produced by all electrical circuits
working above the absolute zero. Noise cannot be
eliminated but only minimised.

NTSC
National Television System Committee, an American
committee that set the standards for colour television
as used today in USA,
Canada,
Japan and a few other countries.

O/P
Output. Objective. The very first optical element
at the front of a lens.

OCULAR
The very last optical element at the back of a lens
(the one closer to the CCD chip).

OSCILLOSCOPE
(Also CRO, from "Cathode Ray Oscilloscope").
An electronic device that can measure the signal
changes versus time. A must for any CCTV technician.

PAN AND TILT HEAD
(P/T head). A motorised unit permitting vertical
and horizontal positioning of a camera and lens
combination. Usually 24 VAC motors are used in such
P/T heads, but also 110 VAC, ie. 240 VAC units can
be ordered.

PHOT
A photometric light unit for very strong illumination
levels. One phot is equal to 10,000 luxes.

PHOTODIODE
A type of semiconductor device in which a PN junction
diode acts as a photo sensor.

PHOTO-EFFECT
Also known as photoelectric effect. This refers
to a phenomenon of ejection of electrons from a
metal whose surface is exposed to light. Photon.
A representative of the quantum nature of light.
It is considered as the smallest unit of light.

PHOTOPIC VISION
The range of light intensities, from 105 lux down
to nearly 10-2 lux, detectable by the human eye.

PINHOLE LENS
A fixed focal length lens, for viewing through a
very small aperture, used in discrete surveillance
situations. The lens normally has no focusing control
but offers a choice of iris functions.

PIXEL
Derived from picture element. Usually refers to
the CCD chip unit picture cell. It consists of a
photo sensor plus its associated control gates.

PLUMBICON
Thermionic vacuum tube developed by Philips, using
a lead oxide photoconductive layer. It represented
the ultimate imaging device up to the introduction
of CCD chips.

POLARISING FILTER
An optical filter that transmits light in only one
direction (perpendicular to the light path), out
of 360В° possible. The effect is such that it can
eliminate some unwanted bright areas or reflections,
such as when looking through a glass window. In
photography, polarising filters are used very often
to darken a blue sky.

POTS
Plain Old Telephone Service, ie. the telephone service
in common use throughout the world today. Also known
as PSTN.

PRESET POSITIONING
A function of a pan and tilt unit, including the
zoom lens, where a number of certain viewing positions
can be stored in the systems' memory (usually this
is in the PTZ site driver) and recalled when required,
either upon an alarm trigger, programmed or manual
recall.
PRINCIPLE POINT
An optical term that refers to one of the two points
that each lens has along the optical axis. The principle
point closer to the imaging device (CCD chip in
our case) is used as a reference point when measuring
the focal length of a lens.

PSTN
Public Switched Telephone Network usually refers
to the "plain old telephone" service.
Also known as POTS.

PTZ SITE DRIVER
(PTZ site receiver, or decoder). An electronic device,
usually a part of a video matrix switcher, which
receives digital, encoded control signals in order
to operate pan, tilt, zoom and focus functions.

QUAD COMPRESSOR
(Also split screen unit). Equipment which simultaneously
displays parts or more than one image on a single
monitor. It usually refers to four quadrants display.

RAID
Redundant Arrays of Independent Disks. This a technology
of connecting a number of hard drives into one mass
storage device, which can be used, among other things,
for digital recording of video images.

RAM
Random Access Memory. An electronic chip, usually
known as "memory", holding digital information
while there is power applied to it. Its capacity
is measured in kilobytes.

RANDOM INTERLACE
A term describing a camera that has a free running
horizontal sync as opposed to a 2:1 interlace type
which has the sync locked and therefore has both
fields in a frame interlocked together accurately.

REMOTE CONTROL
A transmission and receiving of signals for controlling
remote devices such as pan and tilt units, lens
functions, wash and wipe control and similar.

RETMA
Former name of the EIA association. Some older video
test charts carry the name "RETMA Chart".

RF SIGNAL
Radio frequency signal that belongs to the region
up to 300GHz.

RG-11
A video coaxial cable with 75 Ohms impedance and
much thicker diameter than the popular RG-59 (of
approximately 12
mm). With RG-11 much longer distances can be achieved
(at least twice the RG-59), but it is more expensive
and harder to work with.

RG-58
A coaxial cable designed with 50 Ohms impedance,
therefore not suitable for CCTV. Very similar to
RG-59, only slightly thinner.

RG-59
A type of coaxial cable that is most common in use
in small to medium size CCTV systems. It is designed
with an impedance of 75 Ohms. It has an outer diameter
of around 6
mm and it is a good compromise between maximum distances
achievable (up to 300 m for monochrome signal, and 250
m for colour) and good transmission.

RMS
An abbreviation for Root Mean Square. All AC voltages
are measured with multimeters that show the RMS
value of the signal (not the peaks). For a sine
wave signal such as the mains, the RMS value happens
to be 1.41 times (square root of 2) below the peak
values.

ROM
Read Only Memory. An electronic chip, containing
digital information that does not disappear when
power is turned off.

RS-232
A format of digital communication where only two
wires are required. It is also known as a serial
data communication. The RS-232 standard defines
a scheme for asynchronous communications, but it
does not define how the data should be represented
by the bits, ie. it does not define the overall
message format and protocol. It is very often used
in CCTV communications between keyboards and matrix
switchers, or between matrix switchers and PTZ site
drivers. The advantage of RS-232 over others is
in its simplicity and use of only two wires.

RS-422
This is an advanced format of digital communication
when compared to RS-232. The basic difference is
in the need for four wires instead of two as the
communications is not single-ended as with RS-232,
but differential. In simple terms, the signal transmitted
is "read" at the receiving end as the
difference between the two wires without common
earth. So if there is noise induced along the line,
it will be cancelled out. The RS-422 can drive lines
of over a kilometre in length and distribute data
to up to 10 receivers.

RS-485
This is an advanced format of digital communications
compared to RS-422. The major improvement is in
the number of receivers that can be driven with
this format, and this is up to 32.

S/N RATIO
Signal-to-Noise ratio is calculated with the logarithm
of the normal signal and the noise RMS value.

SCENE ILLUMINATION
The average light level incident upon a protected
area. Normally measured for the visible spectrum
with a light meter having a spectral response corresponding
closely to that of the human eye and is quoted in
lux. Scotopic Vision levels are illumination levels
below 10-2 lux, thus invisible to the human eye.
Silicon. The raw material of which modern semiconductor
devices are made.

SIMPLEX
In general, it refers to a communications system
that can transmit information in one direction only.
In CCTV, simplex is used to describe a method of
multiplexer operation where only one function can
be performed at a time, eg. either recording or
playback individually.

SKIN EFFECT
The tendency of alternating current to travel only
on the surface of a conductor as its frequency increases.

SLOW SCAN
The transmission of a series of frozen images by
means of analog or digital signals over limited
bandwidth media, usually telephone.

SMEAR
An unwanted side effect of vertical charge transfer
in a CCD chip. It shows vertical bright stripes
in places of the image where there are very bright
areas. In better cameras smear is minimised to almost
undetectable levels.

SMPTE
Society of Motion Picture and Television Engineers.
Spectrum analyser. An electronic device that can
show the spectrum of an electric signal.

SPECTRUM
In Electromagnetics, spectrum refers to the description
of a signal's amplitude versus its frequency components.
In optics, spectrum refers to the light frequencies
composing the "white light" which can
be seen as rainbow colours.

SPLIT SCREEN UNIT
(Quad compressor). Equipment which simultaneously
displays parts or more than one image on a single
monitor. It usually refers to four quadrants display.

S-VHS
Super VHS format of video recording. A newer standard
proposed by JVC, preserving the downward compatibility
with the VHS format. It offers much better horizontal
resolution up to 400 TV lines. This is mainly due
to the colour separation techniques, high quality
video heads and better tapes. Sync. This is short
from synchronisation pulse.

TBC
Time Base Correction. Refers to the synchronisation
of various signals inside a device such as a multiplexer
or a TBC Corrector.

TDG
Short for time and date generator.

TELEMETRY
Remote controlling system of, usually, digital encoded
data, intended to control pan, tilt, zoom, focus,
preset positions, wash, wipe and similar. Being
digital, it is usually sent via twisted pair cable,
or coaxial cable together with the video signal.

TERMINATION
This usually refers to the physical act of terminating
a cable with a special connector, which for coaxial
cable is, usually, BNC. For fibre optic cable this
is the ST connector. It can also refer to the impedance
matching when electrical transmission is in use.
This is especially important for high frequency
signals, such as the video signal, where the characteristic
impedance is accepted to be 75 Ohms.

TIME LAPSE VCR
(TL VCR). A video recorder, most often in VHS format,
that can prolong the video recording on a single
tape up to 960 hours (this refers to a 180 min tape).
This type of VCRs are very often used in CCTV systems.
The principle of operation is very simple - instead
of having the video tape travel at a constant speed
of 2.275 cm/s (which is the case with the domestic
models of VHS VCRs), it moves with discrete steps
which can be controlled. Time Lapse VCRs have a
number of other special functions very useful in
CCTV, such as external alarm trigger, time and date
superimposed on the video signal, alarm search and
so on.

TIME LAPSE VIDEO RECORDING
The intermittent recording of video signals at intervals
to extend the recording time of the recording medium.
It is usually measured in reference to a 3 hr (180
min) tape.

TIME MULTIPLEXING
The technique of recording several cameras onto,
usually, one time lapse VCR by sequentially sending
camera pictures with a timed interval delay to match
the time lapse mode selected on the recorder.

UHF SIGNAL
Ultra high frequency signal. In television it is
defined to belong in the radio spectrum between
470 MHz and 850 MHz. Unbalanced signal. In CCTV,
this refers to a type of video signal transmission
through a coaxial cable. It is called unbalanced
because the signal travels through the centre core
only, while the cable shield is used for equating
the two voltage potentials between the coaxial cable
ends.

UPS
Uninterruptible power supply. These are power supplies
used in the majority of high security systems, whose
purpose is to back-up the system for at least 10
minutes without mains power. The duration of this
depends on the size of the UPS, usually expressed
in VA, and the current consumption of the system
itself.

VDA
Video Distribution Amplifier. A device that provides
multiple outputs from one video signal such that
interference to one output will not affect others.

VERTICAL SHIFT REGISTER
The mechanism in CCD technology whereby charge is
read out from the photo sensors of an Interline
Transfer or Frame Interline Transfer sensor.

VHF
Stands for Very High Frequency. A signal encompassing
frequencies between 30 and 300 MHz. In television,
VHF Band I uses frequencies between 45 MHz and 67
MHz, and between 180 MHz and 215 MHz for Band III.
Band II is reserved for FM radio from 88 MHz to
108 MHz.

VHS
Stands for Video Home System, as proposed by JVC,
a video recording format that is most often used
in homes, but also in CCTV. It has its own limitations
due to the concept itself, the speed of recording,
the magnetic tapes used and the colour separation
technique. Most of the CCTV equipment today supersedes
VHS resolution.

VIDEO EQUALISATION CORRECTOR
(Video Equaliser). A device which corrects for unequal
frequency losses and/or phase errors in the transmission
of a video signal. Video frame store. A device which
enables digital storage of one or more images for
steady display on a video monitor.

VIDEO MATRIX SWITCHER
(VMS). A device for switching more than one camera,
VCR, video printer and similar, to more than one
monitor, VCR, video printer and similar. Much more
complex and more powerful than video switchers.

VIDEO MONITOR
A device for converting a video signal into an image.

VIDEO PRINTER
A device for converting a video signal to a hard
copy printout. It could be a monochrome (B/W) or
colour. They come in different format sizes. Special
paper is needed.

VIDEO SIGNAL
An electrical signal containing all of the elements
of the image produced by a camera or any other source
of video information.

VIDEO SWITCHER
A device for switching more than one camera to one
or more monitors manually, automatically or upon
receipt of an alarm condition.

VITS
Video Insertion Test Signals. Special shaped electronic
signals inserted in the "invisible" lines
(in the case of PAL, lines 17, 18, 330 and 331)
that are used to determine the quality of reception.

VLF
Very Low Frequency. Refers to the frequencies in
the band between 10 and 30 kHz.

About
the Author:

Instrom Limited is
an independent security consultancy set-up in 1998
to provide a range of impartial security consultancy
services to commerce, industry and the public sector.
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Security Consultant